2d Generation Electric Hearts Will Free Recipient From Bond To

Machine

RESEARCHERS SOON will implant electrically-powered mechanical hearts that will make the pneumatically driven Jarvik-7 heart, implanted in six people so far, look like a Model T.

These ``second generation`` electric hearts will be implanted completely within the recipient`s body, free of bonds to external machines. Recipients of the air-powered Jarvik-7 are tethered by plastic tubes to a 375-pound drive system.

Researchers also say that these newer hearts will be less likely to produce blood clots that apparently caused strokes in four of the six recipients of the Jarvik-7. In addition, an electronic component automatically will control the heart rate, which quickens when the recipient climbs stairs, for example. The rate of the Jarvik-7 must be adjusted by physicians.

``The Jarvik-7 is middle-1970s technology,`` said William Smith, an engineer working on electric hearts at the Cleveland (Ohio) Clinic Foundation. Researchers plan to begin experimental implants of the electric hearts in humans as early as 1991 and hope that they will be approved for general use a few years later. A related electric heart development--the left ventricular assist device (LVAD)--will be implanted in humans experimentally in two years and may be approved for general use in five years.

The electric heart will allow victims in the late stages of heart disease to return to near-normal life, said Gerson Rosenberg, who is directing the development of an electric heart and LVAD at Pennsylvania State University in Hershey. ``They`ll be able to climb steps, go golfing`` and in many cases return to work, he said.

The heart will be powered by a rechargeable battery pack that will be worn around the waist or in a vest. The battery pack will be recharged by plugging it into a wall outlet or the cigarette lighter in a car, Rosenberg said.

In 1983, Penn State researchers implanted an electric heart in a calf named ``E.T.,`` short for Electric Total. E.T. lived 222 days without evidence of organ dysfunction and was able to exercise outdoors with a portable battery pack. The calf died when an electronic component that regulated the heart rate failed.

A panel of experts convened recently by the National Heart, Lung and Blood Institute, estimated that each year between 17,000 and 35,000 people under age 70 could benefit from the implantation of an artificial heart or LVAD.

The panel projected that the average recipient would live 54 months with the device, and that hospital and follow-up costs would reach $150,000.

The LVAD is a pump that assists, rather than replaces, the heart`s left ventricle, which does about 80 percent of the heart`s work. The natural left ventricle pumps the blood into the LVAD, which then pumps the blood through the circulatory system.

A major advantage of the LVAD is that should the device fail, the natural heart still would be in place and may be able to sustain circulation until the LVAD can be replaced. The artificial heart has no such backup.

Researchers say LVADs will be used for patients whose left ventricle is weakened but still functioning. The total artificial heart will be used in patients whose heart has failed completely. Because both devices are pumps, some centers are developing both, using the electric LVAD as a precursor to the electric total artificial heart. ``You use the same technology to build both devices,`` Smith explained.

Four makers of electric LVADs have received funding from the National Heart, Lung and Blood Institute to begin preclinical testing of their devices. Because reliability is such an important criterion for a blood pump, the LVADs will be expected to run in a laboratory for two years with a failure rate of less than 20 percent. Models that pass the preclinical tests probably will be implanted experimentally in humans in 1987 or 1988. If the clinical trials go well, the LVADs may be approved for general use by 1990 or 1991, researchers say.

The electric heart will require between 10 and 20 watts of power, which is about a million times the power required by a pacemaker. This is the reason recipients will have to wear a battery pack.

In early designs, the battery pack was connected to the electric blood pump by a wire that pierced the skin. Like the pneumatic tubes that power the Jarvik-7, the wire posed the danger of infection at its point of entry.

In the four LVADs being developed now, the electricity is passed through the skin without a wire. An electric coil, connected to the battery pack, is worn on the surface of the skin; another coil, implanted just below the skin, receives the electrical current inductively and sends it to the electric motor.

In most designs, a small battery is implanted with the electric blood pump. This battery will be strong enough to power the pump without the external battery pack for short periods--perhaps 30 to 45 minutes, enough time for the recipient to take a shower.